Since September 11, 2001, conversions to Islam have worried strategic analysts, as neophytes are usually considered to be more extremist than traditional Muslims. The author argues that a distinction must be made between (1) conversion from one religion to another, (2) 'internal' conversion (a 'born-again' phenomenon for Christians), and (3) the discovery of God, especially for animists in Africa or atheists and agnostics in the West. When these types are considered together, the expansion of Islam in Africa remains mysterious, not only because its appeal would need further investigation to be fully understood, but also because it raises doubts as to the reality of its growth. Hence this paper challenges common assumptions, arguing that there is no scientific measurement of the progression of Islam in Africa. Nigeria, the most populous country on the continent, is an interesting case study in this regard, because it has experienced many religious confrontations between Muslims in the North and Christians in the South. In the first part of the article, the author shows that there are no rational proofs about the growth of Islam, only clues. In the second part, he questions the development of Islam among non-Muslim societies, as compared to the rapid propagation of Christianity in the Middle Belt of the country. In the third part, he analyses political conversions to Islam in the South, where Muslims constitute a minority of the population. Focusing on Asari Dokubo and his Niger Delta People's Volunteer Force, a group that demands local autonomy, the author aims to understand the attraction of Islam for gangsters or warlords who oppose a Christian elite. Their conversion seems quite paradoxical because it can repulse their non-Muslim followers. Bibliogr., notes, ref., sum. [Journal abstract]